1. Field of the Invention
The present invention relates to a magnetic disk apparatus and more particularly, is applicable to, for example, a floppy disk driving device.
2. Description of the Related Art
Conventionally, this type of floppy disk driving device is adapted to drive a magnetic head by a magnetic head driving circuit which is formed as an integrated circuit to be an integral part thereof and furthermore to process a reproduced signal output from the magnetic head. Since its usefulness is greatly improved if such a magnetic head driving circuit may be used in common by various types of equipment, this type of magnetic head driving circuit is adapted to be capable of switching its operating conditions by providing an external switching means.
In particular, the conventional magnetic head driving circuit is adapted to be capable of setting its recording current to two levels depending on whether a predetermined terminal is connected to a ground or not, the switching of such a connection being effected by replacing a jumper plug. Further, other characteristics, such as the cut-off frequency of a lowpass filter for limiting the bandwidth of reproduced signals and an emitting color of an light-emitting diode for indicating an operating condition can be likewise switched by replacing a jumper plug. Thereby the conventional magnetic head driving circuit is adapted to be capable of being used for various types of equipment as an entire circuit board having a magnetic driving circuit implemented thereon or as an entire floppy disk driving device by simply changing a jumper plug to be plugged in.
This type of floppy disk driving device is inclined to intensify a peak shift, as the recording current is increased, although an overwrite is securely effected. For this reason, it is desirable in this type of floppy disk driving device to set the recording current to an optimum value, while such optimum value is different for each magnetic head. In this regard, there is a method in which the peak shift is corrected by correcting the timing of recording data, where the optimum value of such correction amount itself, too, varies by each magnetic head according to the recording current. Further, an optimum value with respect to the cut-off frequency of the low-pass filter for limiting the bandwidth of a reproduced signal also varies by each magnetic head.
Accordingly, it is presumed that, if these operating conditions can be switched in a detailed manner, desired recording data may be recorded and reproduced accurately at a high density. In the conventional magnetic head driving circuit, however, if the operating conditions are minutely switched by replacing jumper plugs, then replacing the jumper plugs becomes correspondingly difficult and there is also a problem of erroneously setting the operating conditions. Further, if the operating conditions are to be minutely switched by replacing jumper plugs in this manner, wiring of the peripheral patterns of the jumper plugs becomes complicated, resulting in a problem that the circuit board is correspondingly increased in size.
Although a method in which the operating conditions are switched by changing positions of soldering instead of using jumper plugs has been considered, it is not yet satisfactory for practical use because of degradation in reliability associated with the changing of the soldering positions is possible.